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Project Title: Evaluation of Fuel Tank Drop Tests and ASTM Tensile Tests conducted by Southwest Research Institute Date: December 13, 2004 Submitted To:

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Presentation on theme: "Project Title: Evaluation of Fuel Tank Drop Tests and ASTM Tensile Tests conducted by Southwest Research Institute Date: December 13, 2004 Submitted To:"— Presentation transcript:

1 Project Title: Evaluation of Fuel Tank Drop Tests and ASTM Tensile Tests conducted by Southwest Research Institute Date: December 13, 2004 Submitted To: Dr. Kennerly H. Digges, MVFRI Mr. R. Rhoads Stephenson Prepared By: Dr. Nabih E. Bedewi Progress Report No. 3 Final

2 OUTLINE Questions to be Answered by Study Questions to be Answered by Study Review of SwRI Tests Review of SwRI Tests o Types of Fuel Tanks Tested o Drop Tests o Material Coupon Testing Nonlinear Finite Element Simulations Nonlinear Finite Element Simulations o Model Development o Assumptions

3 OUTLINE (cont.) Simulation of Plymouth Grand Voyager Tank Simulation of Plymouth Grand Voyager Tank o Model Development o Simulation Results and Comparison to SwRI Test o Summary of Simulation Results Comparison of Generic Shape Tanks Comparison of Generic Shape Tanks o Rectangular Tank Simulation Results and Comparison to SwRI Test o Rectangular Tank with a Neck o Small Rectangular Tank o Summary of Simulation Results

4 OUTLINE (cont.) Simulation of Different Coupon Tests Simulation of Different Coupon Tests o SwRI Simple Tensile Test o Hydrostatic Pressure on a Curved Coupon o Combined Loading on a Curved Coupon Simulation of Plymouth Tank with Gasoline Properties Simulation of Plymouth Tank with Gasoline Properties o Drop Test Simulation o Side Impact Simulation Conclusions and Proposed Future Research Conclusions and Proposed Future Research o Further Simulation Studies o Proposed Testing Program

5 Questions to be Answered Is there an aging effect on the structural integrity of the plastic fuel tanks? Is there an aging effect on the structural integrity of the plastic fuel tanks? If so, do the geometry of the tank, type of plastic, and pinch off strength have an influence on the structural integrity? If so, do the geometry of the tank, type of plastic, and pinch off strength have an influence on the structural integrity? Are the tensile tests that were conducted by SwRI adequate to replicate the loads seen in the drop tests to assess the strength of the pinch off? Are the tensile tests that were conducted by SwRI adequate to replicate the loads seen in the drop tests to assess the strength of the pinch off? What additional tests, if any, should be carried out to complete the evaluation and make final conclusions? What additional tests, if any, should be carried out to complete the evaluation and make final conclusions?

6 Resources Used SwRI final report was reviewed in detail Emphasis was placed on test conditions, photographs of undamaged and damaged tanks, description of results and conclusions Biokinetics reports I and II were also reviewed to understand how different test regulations and standards address aging and fuel effects The following SAE papers were also obtained and reviewed in detail:

7 Papers Reviewed Crash-Resistant Fuel Tanks for Helicopters and General Aviation Aircraft, SAE740358, 1974 Crash-Resistant Fuel Tanks for Helicopters and General Aviation Aircraft, SAE740358, 1974 Development of Plastic Fuel Tanks Using Modified Multi-Layer Blow Molding, SAE , 1990 Development of Plastic Fuel Tanks Using Modified Multi-Layer Blow Molding, SAE , 1990 Development of High Capacity Plastic Fuel Tanks for Trucks, SAE921513, 1992 Development of High Capacity Plastic Fuel Tanks for Trucks, SAE921513, 1992 Comparative Life Cycle Assessment of Plastic and Steel Vehicle Fuel Tanks, SAE982224, 1998 Comparative Life Cycle Assessment of Plastic and Steel Vehicle Fuel Tanks, SAE982224, 1998

8 Simulation Studies of Sloshing in a Fuel Tank, SAE , 2002 Simulation Studies of Sloshing in a Fuel Tank, SAE , 2002 Structural and Material Features that Influence Emissions from Thermoplastic Multilayer Fuel Tanks, SAE , 2003 Structural and Material Features that Influence Emissions from Thermoplastic Multilayer Fuel Tanks, SAE , 2003 Low Permeation Technologies for Plastic Fuel Tanks, SAE , 2003 Low Permeation Technologies for Plastic Fuel Tanks, SAE , 2003 Papers Reviewed

9 Review of SwRI Tests The following information is extracted directly from the SwRI test report

10 Jeep Grand Cherokee Typical of some SUV tanks mounted behind the rear axle Types of Fuel Tanks RECTANGULAR * The Saturn tank tested is also rectangular but smaller and with thinner profile

11 Plymouth Grand Voyager Typical of tanks with a narrow shape mounted inside the frame rail and in front of the rear axle or rear suspension RECTANGULAR WITH A NECK Types of Fuel Tanks

12 Accordance with U.S. DOT 49 CFR , Section E Drop Test. The Section E Drop Test of the referenced standard states that the fuel tanks shall be filled with a quantity of water having a weight equal to the weight of the maximum fuel load of the tank. The fuel tank is filled then dropped from a 30 ft elevation to assess the durability of the fuel tanks and measure the leak rate. After filling the fuel tank with a quantity of water having a weight equal to the weight of the maximum fuel load and selecting the vulnerable point of impact, the fuel tank was then positioned and strapped to the drop apparatus before being hoisted. Drop Test

13 DROP TEST SETUP SwRIs Department of Fire Technologys Test Facility, located in San Antonio, Texas Drop Test

14 RECTANGULAR TANK PRE AND POST IMPACT

15 Leakage of Conditioned Plymouth Plastic Fuel Tank After Severe Drop RECTANGULAR TANK WITH A NECK PRE-POST IMPACT Drop Test

16 TENSILE TEST ASTM D , Standard Test Method for Tensile Properties of Plastics Typical Tensile Test Specimen Coupon Thickest Region at Pinch-Off Location Material Testing Voyager Cherokee

17 Typical Tensile Test Setup As these coupons were extracted from the fuel tanks, the pinch-off location in each was perpendicular to the long-axis of the specimen parent material. The overall length of the specimen coupons depended on the location of extraction and ranged from 6 in. to 9 in. in length. The thickness of the specimen coupons varied as well, ranging from 0.2 in. to 0.5 in. For all specimen coupons, the thickest region was at the pinch-off location. Material Testing

18 Typical Axial Load Per Unit Width Versus Displacement Diagram Material Testing

19 Nonlinear Finite Element Simulations Model Development and Assumptions

20 Model Development Several finite element models were initially analyzed for different geometry tanks of both plastic and steel composition to understand the behavior and assess the importance of the fluid/structure interaction Several finite element models were initially analyzed for different geometry tanks of both plastic and steel composition to understand the behavior and assess the importance of the fluid/structure interaction Some of the tank models existed already in public domain vehicle models developed for NHTSA while others were developed specifically for this study, as outlined later Some of the tank models existed already in public domain vehicle models developed for NHTSA while others were developed specifically for this study, as outlined later

21 Simulation Background Tank Models Analyzed Initially Chevy C-2500 TruckToyota RAV 4 Ford EconolineFord Taurus

22 Effect of Water Simulation with no Water in the Tank (i.e. mass of water included but not the fluid-structure interaction) Deformation at impact point is accurate, but bulging of tank and stress buildup in non-impact points is not represented

23 Modeling Water in the Tank A new method based on mesh-free elements (SPH) in LS-DYNA was used to model the fluid-structure interaction in the tank

24 Modeling Water in the Tank Simulation with water effects Deformation at impact point is accurate as well as bulging of tank and stress buildup in non-impact points

25 Modeling Water in the Tank Simulation with water effects Deformation at impact point is accurate as well as bulging of tank and stress buildup in non-impact points

26 Model Development This numerical model contains high-end simulation tools which are sophisticated and require specialized expertise to develop and use This numerical model contains high-end simulation tools which are sophisticated and require specialized expertise to develop and use Development of such a simulation model was challenging because there are no systematic tools available for creating and setting-up the coupling between the conventional finite element and the mesh-free (SPH) model, requiring extra attention and significant amounts of effort and time Development of such a simulation model was challenging because there are no systematic tools available for creating and setting-up the coupling between the conventional finite element and the mesh-free (SPH) model, requiring extra attention and significant amounts of effort and time Several initial simulations were conducted to improve and optimize the robustness, efficiency and accuracy of the model. Some of the parameters that were investigated included: particle density, smoothing length, viscosity coefficient, and material parameters Several initial simulations were conducted to improve and optimize the robustness, efficiency and accuracy of the model. Some of the parameters that were investigated included: particle density, smoothing length, viscosity coefficient, and material parameters Preliminary simulations were performed to ensure that the fluid (water) is at equilibrium prior to impact, and the final state was used as the initial state for the drop test simulations Preliminary simulations were performed to ensure that the fluid (water) is at equilibrium prior to impact, and the final state was used as the initial state for the drop test simulations

27 Model Development Initial simulation results using the material data extracted from the coupon tests performed by SwRI showed significantly more deformation compared with the drop test results. After a literature survey on High Density Poly-Ethylene fuel tank material properties a more accurate material data set was used which gave closer results to the drop tests Initial simulation results using the material data extracted from the coupon tests performed by SwRI showed significantly more deformation compared with the drop test results. After a literature survey on High Density Poly-Ethylene fuel tank material properties a more accurate material data set was used which gave closer results to the drop tests Since the pinch-off region played an important role in the behavior of the fuel tank, extra attention was given to model this area. To represent the exact cross-section and stiffness properties, five sets of beam elements were used around the tank. This technique is selected also to monitor the forces in this region Since the pinch-off region played an important role in the behavior of the fuel tank, extra attention was given to model this area. To represent the exact cross-section and stiffness properties, five sets of beam elements were used around the tank. This technique is selected also to monitor the forces in this region Tanks were filled with water up to 74% capacity of the total volume

28 Modeling the Pinch-off To model the pinch-off regions, equivalent beam cross-sections were used with geometry properties extracted from the specimen pictures. Circular beams were modeled all around the tank with mm and mm radii. An average value of 0.4 in (10 mm) is used across the whole tank as the thickness value, where the thickness changes between 0.2 in and 0.5 in.

29 Material model and properties used for Poly-Ethylene plastic o Piecewise Linear Plasticity Constitutive Model o Density: 0.95E-9 Tons/mm 3 o Elastic Modulus: 1200 N/mm 2 o Poissons Ratio: 0.3 o Yield Stress: 30 N/mm 2 o Tangent Modulus: 12 N/mm 2 o Cowper and Symonds strain rate effects with C=90 and P=4.5 Material model and properties for water o Elastic Fluid (using SPH) o Density: 0.996E-9 Tons/mm 3 o Poissons Ratio: 0.5 o Bulk Modulus: 2250 N/mm 2 Material Properties of the Model

30 Simulation of Plymouth Grand Voyager Tank Model Development and Comparison with SwRI Drop Test

31 Extraction of Tank Geometry Digitized Voyager (Caravan) Tank

32 Grand Voyager Tank FINITE ELEMENT MODEL OF THE TANK The total weight of the tank is 73 kg of which 56 kg is the water weight

33 COUPLED FINITE ELEMENT AND MESHLESS MODEL Grand Voyager Tank Various views of front side

34 COUPLED FINITE ELEMENT AND MESHLESS MODEL Grand Voyager Tank Various views of back side

35 DETAILED PINCH-OFF REGION Grand Voyager Tank

36 DETAILED PINCH-OFF REGION Grand Voyager Tank Three rows of beam elements parallel to pinch-off joint Two rows of beam elements perpendicular to pinch-off joint Force measurement direction

37 MODEL DETAILS Grand Voyager Tank Number of Parts11 Number of Shell Elements16,876 Number of Beam Elements1,717 Number of Nodes16,572 Number of SPH Particles124,198 Final Simulation Time0.1 sec. Number of Processors4 Computation Time15 hrs

38 ELEMENT PRESSURE Simulation of Grand Voyager Tank Drop Test

39 DEFORMATION-SLOSHING Simulation of Grand Voyager Tank Drop Test

40 DEFORMATION-SLOSHING Simulation of Grand Voyager Tank Drop Test

41 IMPACT REACTION FORCE ON THE GROUND AT POINT OF IMPACT Simulation of Grand Voyager Tank Drop Test

42 INTERNAL PRESSURE ON TANK WALL AT SELECTED ELEMENT Simulation of Grand Voyager Tank Drop Test

43 The next series of slides show the results of the forces as measured by the five sets of beam elements; i.e. the forces observed at the pinch-off region during the impact

44 PINCH-OFF EVALUATION BEAM SET-I Beam Element Data of Grand Voyager Tank Notice red spot (high loads) at the neck area Click mouse on image to repeat

45 COMPARISON WITH SwRI DROP TEST: FAILURE OCCURRED IN HIGH LOAD NECK AREA AS PREDICTED BY THE MODEL Beam Element Data of Grand Voyager Tank

46 Region with maximum force

47 PINCH-OFF EVALUATION BEAM SET-II Beam Element Data of Grand Voyager Tank

48

49 PINCH-OFF EVALUATION BEAM SET-III Beam Element Data of Grand Voyager Tank

50

51 PINCH-OFF EVALUATION BEAM SET-IV Beam Element Data of Grand Voyager Tank

52

53 PINCH-OFF EVALUATION BEAM SET-V Beam Element Data of Grand Voyager Tank

54

55 MAXIMUM AXIAL FORCES FOUND AT DIFFERENT BEAM ELEMENTS AT THE PINCH-OFF REGION Beam Element Data of Grand Voyager Tank Peak force in perpendicular direction approx. 3,500 N (780 LB)

56 Summary of Simulation Results Plymouth Grand Voyager Tank The FE analysis predicted the maximum loads at the same location where the pinch-off region ruptured in the test The FE analysis predicted the maximum loads at the same location where the pinch-off region ruptured in the test As expected, the maximum force occurred in the tank neck area since the cross section of the tank is narrower leading to increased water pressure and larger buckling load As expected, the maximum force occurred in the tank neck area since the cross section of the tank is narrower leading to increased water pressure and larger buckling load The maximum force predicted is perpendicular to the pinch off joint and is approximately 780 LB (this is 40% higher than the force that failed the specimens in the tensile tests performed by SwRI) The maximum force predicted is perpendicular to the pinch off joint and is approximately 780 LB (this is 40% higher than the force that failed the specimens in the tensile tests performed by SwRI) The peak force occurred at about 0.02 sec hence the strain rate effect is important (SwRI tensile test peaked in 1.2 min) The peak force occurred at about 0.02 sec hence the strain rate effect is important (SwRI tensile test peaked in 1.2 min)

57 Comparison of Generic Shape Tanks

58 Generic Tank Simulations The purpose of this set of simulations is to investigate the effect of tank geometry on the forces generated at the joint The purpose of this set of simulations is to investigate the effect of tank geometry on the forces generated at the joint The following three tanks were modeled: The following three tanks were modeled: o Rectangular tank of similar size as the Voyager tank without neck (this represents the class of tanks such as the Jeep Grand Cherokee) o Same size as above tank but with a neck section (this represents the class of tanks such as the Plymouth Grand Voyager) o Rectangular tank with smaller dimensions than first tank (this represents the class of tanks such as the Saturn) In all cases the thickness of the tank walls and the material properties were kept the same as the Voyager model

59 MODEL DETAILS Number of Parts10 Number of Shell Elements18,049 Number of Beam Elements1,680 Number of Nodes18,051 Number of SPH Particles102,259 Final Simulation Time0.2 sec. Number of Processors6 Computation Time28 hrs Generic Tank Model Weight: Rectangular baseline tank: 75 kg of which 56 kg is water Rectangular tank with neck: 75 kg of which 56 kg is water Rectangular small tank: 48 kg of which 33 kg is water

60 Rectangular Tank (Baseline) DEFORMATION-SLOSHING

61 Rectangular Tank (Baseline)

62 PINCH-OFF EVALUATION BEAM SET-I Rectangular Tank (Baseline)

63 PINCH-OFF EVALUATION BEAM SET-II Rectangular Tank (Baseline)

64 PINCH-OFF EVALUATION BEAM SET-III Rectangular Tank (Baseline)

65 PINCH-OFF EVALUATION BEAM SET-IV Rectangular Tank (Baseline) Peak tensile (+ve) forces (red contours) occur at or near the impact point

66 PINCH-OFF EVALUATION BEAM SET-V Rectangular Tank (Baseline)

67 FAILURE IN SwRI JEEP CHEROKEE TEST Rectangular Tank (Baseline)

68 Rectangular Tank with a Neck DEFORMATION-SLOSHING

69 Rectangular Tank with a Neck

70 PINCH-OFF EVALUATION BEAM SET-I Rectangular Tank with a Neck

71 PINCH-OFF EVALUATION BEAM SET-II Rectangular Tank with a Neck

72 PINCH-OFF EVALUATION BEAM SET-III Rectangular Tank with a Neck

73 PINCH-OFF EVALUATION BEAM SET-IV Rectangular Tank with a Neck

74 PINCH-OFF EVALUATION BEAM SET-V Rectangular Tank with a Neck

75 DEFORMATION-SLOSHING Small Rectangular Tank

76 DEFORMATION-SLOSHING Small Rectangular Tank

77 PINCH-OFF EVALUATION BEAM SET-I Small Rectangular Tank

78 PINCH-OFF EVALUATION BEAM SET-II Small Rectangular Tank

79 PINCH-OFF EVALUATION BEAM SET-III Small Rectangular Tank

80 PINCH-OFF EVALUATION BEAM SET-IV Small Rectangular Tank

81 PINCH-OFF EVALUATION BEAM SET-V Small Rectangular Tank

82 Maximum Force Comparisons Tank with Neck Baseline Smaller Tank Tank with neck (Grand Voyager type) Baseline rectangular tank (Jeep Cherokee type) Small rectangular tank (Saturn type)

83 Summary of Simulation Results Generic Shape Tanks The FE analysis predicted the maximum loads near the same location where the pinch-off region ruptured in both the rectangular (Cherokee) and tank with neck (Voyager) tests The FE analysis predicted the maximum loads near the same location where the pinch-off region ruptured in both the rectangular (Cherokee) and tank with neck (Voyager) tests The addition of a neck section in a rectangular tank, keeping everything else similar, increases the forces in the pinch-off region by 50% The addition of a neck section in a rectangular tank, keeping everything else similar, increases the forces in the pinch-off region by 50% Reducing the rectangular tank overall dimensions and mass by 30%, keeping everything else similar, reduces the forces in the pinch-off region by 10% Reducing the rectangular tank overall dimensions and mass by 30%, keeping everything else similar, reduces the forces in the pinch-off region by 10%

84 Summary of Simulation Results (cont.) Generic Shape Tanks The Cherokee pinch-off contact area is 30% of the Voyager pinch-off contact area, therefore for the same amount of force: The Cherokee pinch-off contact area is 30% of the Voyager pinch-off contact area, therefore for the same amount of force: o the stress in the Cherokee joint would be three times higher o the strength of the Cherokee joint would be a third of the Voyagers Since we did not receive the tested tanks from SwRI we cannot make similar conclusions about the Saturn Tank. However, if the contact patch area is somewhere in between the Cherokee and Voyagers, then from the results of the generic tank simulations, the stress in the Saturn joint would be 20% lower than the Cherokees. Since we did not receive the tested tanks from SwRI we cannot make similar conclusions about the Saturn Tank. However, if the contact patch area is somewhere in between the Cherokee and Voyagers, then from the results of the generic tank simulations, the stress in the Saturn joint would be 20% lower than the Cherokees. Voyager pinch-off contact patch Cherokee pinch-off contact patch

85 Simulation of Different Coupon Tests Model Development and Comparison with SwRI Coupon Tests

86 The next series of slides show results of three simulation cases for different coupon tests that were developed to try and force a failure in the pinch-off area. The first scenario is the SwRI tensile test.

87 Simulation of Coupon Tests Specimen FE model based on Voyager tank properties used in all three cases

88 TOP VIEW Applied Force Click on image to see animation Simulation of Coupon Tests CASE I - SIMPLE TENSILE TEST

89 EFFECTIVE STRESS Simulation of Coupon Tests CASE I - SIMPLE TENSILE TEST Click on image to see animation

90 PLASTIC STRAIN Simulation of Coupon Tests CASE I - SIMPLE TENSILE TEST Click on image to see animation

91 Simulation of Coupon Tests CASE II - HYDROSTATIC PRESSURE TEST uniform pressure Reaction force

92 GEOMETRY EXTRACTION Simulation used to obtain curved geometry of Specimen Simulation of Coupon Tests Click on image to see animation CASE II - HYDROSTATIC PRESSURE TEST

93 PRESSURE BOUNDARY CONDITION highest stresses and strains not at joint Simulation of Coupon Tests Click on image to see animation CASE II - HYDROSTATIC PRESSURE TEST

94 Simulation of Coupon Tests CASE III – SPECIMEN WRAPPED AROUND PIPE Fixed Pipe with frictionless surface Applied force

95 USING CYLINDER highest stresses and strains not at joint Simulation of Coupon Tests Click on image to see animation CASE III – SPECIMEN WRAPPED AROUND PIPE

96 Summary of Simulation Results Coupon Tests A simple tensile test such as the one performed by SwRI is not representative because in the drop test the pinch-off joint is subjected to a bidirectional force along, and perpendicular to, the joint A simple tensile test such as the one performed by SwRI is not representative because in the drop test the pinch-off joint is subjected to a bidirectional force along, and perpendicular to, the joint Applying a hydrostatic force on a curved specimen is more representative of the drop test scenario because the primary loads are generated by the water pressure Applying a hydrostatic force on a curved specimen is more representative of the drop test scenario because the primary loads are generated by the water pressure This is not a simple test to perform and therefore an alternative is to place the specimen on a curved low friction device (pipe) and applying a tensile force at the ends This is not a simple test to perform and therefore an alternative is to place the specimen on a curved low friction device (pipe) and applying a tensile force at the ends

97 Summary of Simulation Results (cont.) Coupon Tests The results of the simulations clearly show that the latter provides the same type of load distribution as the hydrostatic case and the stress builds up more at the joint The results of the simulations clearly show that the latter provides the same type of load distribution as the hydrostatic case and the stress builds up more at the joint However, all three cases were not able to generate a higher stress at the joint than the parent material. However, all three cases were not able to generate a higher stress at the joint than the parent material. It is not clear at this point that there exists a simple coupon test that can generate the load conditions to fail the pinch- off joints It is not clear at this point that there exists a simple coupon test that can generate the load conditions to fail the pinch- off joints The models have a limitation in that they do not represent any micro-cracks in the joint which would initiate an early failure when tested The models have a limitation in that they do not represent any micro-cracks in the joint which would initiate an early failure when tested

98 Simulation of Plymouth Tank with Gasoline Properties

99 Simulations with Gasoline The purpose of this set of simulations is to investigate the effect of the gasoline properties on the behavior of the tanks as compared to the water properties The purpose of this set of simulations is to investigate the effect of the gasoline properties on the behavior of the tanks as compared to the water properties The following two scenarios were modeled: The following two scenarios were modeled: o Plymouth Grand Voyager Tank filled 100% with gasoline and dropped from a height of 30 feet similar to the SwRI drop tests. o Same tank and fuel as above except the tank is positioned horizontally and is impacted by a rigid wall traveling at 13.4 m/s (same speed as the impacting tank in a free fall from 30 feet); i.e. gravity is perpendicular to the impact direction.

100 Gasoline Filled Plymouth Tank Vertical Drop

101 Gasoline Filled Plymouth Tank

102 Side Impact Gasoline Filled Plymouth Tank

103 Side Impact Gasoline Filled Plymouth Tank

104 Force Comparisons Forces Parallel to Joint Tank filled with water (74% full) Vertical Drop Tank filled with gasoline (100% full) Vertical Drop Tank filled with gasoline (100% full) Side Impact

105 Force Comparisons Tank filled with water (74% full) Vertical Drop Tank filled with gasoline (100% full) Vertical Drop Tank filled with gasoline (100% full) Side Impact Forces Perpendicular to Joint

106 Summary of Simulation Results Gasoline Filled Tanks The behavior of the tanks when filled with gasoline and dropped from 30 feet or impacted horizontally did not show any difference in the crush behavior or the maximum measured loads (this is perhaps only the case when the tank is filled up to 100% of volume since the effect of gravity on the initial state of the fluid and void does not play a role). The behavior of the tanks when filled with gasoline and dropped from 30 feet or impacted horizontally did not show any difference in the crush behavior or the maximum measured loads (this is perhaps only the case when the tank is filled up to 100% of volume since the effect of gravity on the initial state of the fluid and void does not play a role). The behavior of the tanks when filled with gasoline and dropped from 30 feet did not show any change in terms of the overall tank deformation and the location of the maximum pinch-off area forces when compared to the water filled tanks dropped from 30 feet. The behavior of the tanks when filled with gasoline and dropped from 30 feet did not show any change in terms of the overall tank deformation and the location of the maximum pinch-off area forces when compared to the water filled tanks dropped from 30 feet. However, the force-time history comparison shows an increase for the gasoline tanks in the second peak by about 30% and an increase in the total pulse duration by about 36% (since the crush behavior is the same in both cases then this implies an increase in energy; viz. the area under the force-deflection curve, of 36%). However, the force-time history comparison shows an increase for the gasoline tanks in the second peak by about 30% and an increase in the total pulse duration by about 36% (since the crush behavior is the same in both cases then this implies an increase in energy; viz. the area under the force-deflection curve, of 36%).

107 Conclusions and Proposed Future Research

108 Conclusions At impact the dynamics of the water sloshing causes the water to continue to move down, and since it is an incompressible fluid the tank has to expand At impact the dynamics of the water sloshing causes the water to continue to move down, and since it is an incompressible fluid the tank has to expand The FE analysis predicted the maximum loads at the same location where the pinch-off region ruptured in both tests (neck area in the Voyager and lower edge in Cherokee) The FE analysis predicted the maximum loads at the same location where the pinch-off region ruptured in both tests (neck area in the Voyager and lower edge in Cherokee) A tank with a thin stiff neck, such as the Voyager tank, cannot expand in the neck area leading to increased water pressure and therefore large stresses develop at the joints A tank with a thin stiff neck, such as the Voyager tank, cannot expand in the neck area leading to increased water pressure and therefore large stresses develop at the joints The addition of a neck section in a rectangular tank, keeping everything else similar, increases the forces in the pinch-off region by 50% The addition of a neck section in a rectangular tank, keeping everything else similar, increases the forces in the pinch-off region by 50%

109 The maximum force predicted in the Voyager simulation is perpendicular to the pinch off joint and is approximately 780 LB (this is 40% higher than the force that failed the specimens in the tensile tests performed by SwRI) The maximum force predicted in the Voyager simulation is perpendicular to the pinch off joint and is approximately 780 LB (this is 40% higher than the force that failed the specimens in the tensile tests performed by SwRI) The Jeep Cherokee carries the most amount of fuel of all tanks tested, yet the pinch-off area has the thinnest cross-section (i.e. higher dynamic loads due to water weight and higher stresses due to smaller cross section area) The Jeep Cherokee carries the most amount of fuel of all tanks tested, yet the pinch-off area has the thinnest cross-section (i.e. higher dynamic loads due to water weight and higher stresses due to smaller cross section area) The stress in the Saturn joint is estimated to be 20% lower than the Cherokees. The stress in the Saturn joint is estimated to be 20% lower than the Cherokees. The pinch-off contact area is very important and has a significant effect on the ability of the joint to withstand the impact loads (the size of the Cherokee pinch-off contact area is 30% of the Voyager pinch-off contact area) The pinch-off contact area is very important and has a significant effect on the ability of the joint to withstand the impact loads (the size of the Cherokee pinch-off contact area is 30% of the Voyager pinch-off contact area) Conclusions (cont.)

110 In all cases the peak force occurred at about 0.02 sec hence the strain rate effect is important (SwRI tensile test peaked in 1.2 min) In all cases the peak force occurred at about 0.02 sec hence the strain rate effect is important (SwRI tensile test peaked in 1.2 min) A simple tensile test such as the one performed by SwRI is not representative because in the drop test the pinch-off joint is subjected to a bidirectional force along, and perpendicular to, the joint A simple tensile test such as the one performed by SwRI is not representative because in the drop test the pinch-off joint is subjected to a bidirectional force along, and perpendicular to, the joint It is not clear at this point that there exists a simple coupon test that can generate the load conditions to fail the pinch-off joints It is not clear at this point that there exists a simple coupon test that can generate the load conditions to fail the pinch-off joints The models have a limitation in that they do not represent any micro- cracks in the joint which would initiate an early failure when tested The models have a limitation in that they do not represent any micro- cracks in the joint which would initiate an early failure when tested While a tank filled with water up to 74% volume does represent the general crush behavior of the tank when compared to a tank filled with gasoline up to 100% volume, the maximum forces generated at the pinch- off area could be as much as 10% lower and the total pulse duration as much as 36% less While a tank filled with water up to 74% volume does represent the general crush behavior of the tank when compared to a tank filled with gasoline up to 100% volume, the maximum forces generated at the pinch- off area could be as much as 10% lower and the total pulse duration as much as 36% less Conclusions (cont.)

111 The following two questions may need to be addressed with further simulation studies: The following two questions may need to be addressed with further simulation studies: o The drop test carried out by SwRI is certainly representative of a vehicle impact condition, however, given that the loads that were generated with a gasoline filled tank are more aggressive than those generated by the water filled tank, should the drop height or the amount of water be modified to reflect these changes for a possible future standard test? o Is there some other combination of coupon samples and test configurations that could place the right amount and direction of load on the joint to fail it such that a standard test could exist for testing tank joints? Further Simulation Studies

112 The simulation study clearly shows that there are unique features in each of the tanks tested that some broad conclusions about tank design and testing could be drawn. The simulation study clearly shows that there are unique features in each of the tanks tested that some broad conclusions about tank design and testing could be drawn. While the analysis could explain why certain tank designs have higher loads, and therefore would require thicker tank walls and larger pinch-off contact patch sizes, it did not answer the question as to why the conditioned tanks failed while the new ones did not. While the analysis could explain why certain tank designs have higher loads, and therefore would require thicker tank walls and larger pinch-off contact patch sizes, it did not answer the question as to why the conditioned tanks failed while the new ones did not. It is obvious that exposure to fuel may have some degrading effect on the structural strength of joints. However, the results of the simulations also showed that there are some design considerations which could be addressed to reduce the loads and to strengthen the joints. It is obvious that exposure to fuel may have some degrading effect on the structural strength of joints. However, the results of the simulations also showed that there are some design considerations which could be addressed to reduce the loads and to strengthen the joints. It is believed from the analysis that the tanks tested were subjected to loads at the borderline of the joint strengths. Therefore, more statistically significant tests should be performed. It is believed from the analysis that the tanks tested were subjected to loads at the borderline of the joint strengths. Therefore, more statistically significant tests should be performed. Proposed Testing Program

113 It is proposed to run a set of drop tests to: (a) provide the necessary validation of the FE models, (b) include sufficient statistical significance to get meaningful results, and (c) understand the contribution of fuel exposure in the pinch off area by testing new tanks that have been exposed to fuel for a period of at least 72 hours. The latter is a requirement in a number of fuel tank compliance tests including ECE and military test procedures. It is proposed to run a set of drop tests to: (a) provide the necessary validation of the FE models, (b) include sufficient statistical significance to get meaningful results, and (c) understand the contribution of fuel exposure in the pinch off area by testing new tanks that have been exposed to fuel for a period of at least 72 hours. The latter is a requirement in a number of fuel tank compliance tests including ECE and military test procedures. The proposed program would include the following 46 drop tests: The proposed program would include the following 46 drop tests: Test 1:Custom made clear tank to visualize water slosh and tank bulging effects Tests 2-6:1998 Saturn Twin Cam 4 DrNew tanks (not exposed to fuel) Tests 7-11:1998 Saturn Twin Cam 4 DrNew tanks (filled w/ fuel for 72 hrs) Tests 12-16:1998 Saturn Twin Cam 4 DrReconditioned tanks Tests 17-21:1998 Plymouth Grand VoyagerNew tanks (not exposed to fuel) Tests 22-26:1998 Plymouth Grand VoyagerNew tanks (filled w/ fuel for 72 hrs) Tests 27-31:1998 Plymouth Grand VoyagerReconditioned tanks Tests 32-36:1998 Jeep Grand CherokeeNew tanks (not exposed to fuel) Tests 37-41:1998 Jeep Grand CherokeeNew tanks (filled w/ fuel for 72 hrs) Tests 42-46:1998 Jeep Grand CherokeeReconditioned tanks Proposed Testing Program (cont.)

114 The End


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